How Does a Laser Work?

The word laser is actually an acronym that stands for "light amplified by the stimulated emission of radiation," which is the technical description of how a laser beam is made. In layman's terms, there's a little more to it than that.

For a laser to work, an atom must be stimulated--usually by heat, light or electricity--inside a controlled environment, or lasing medium. Once stimulated, the atom's electrons move from a relaxed or ground state to an excited state. In the relaxed state, electrons orbit closely around the nucleus of an atom. When excited, the electron orbits grow larger, placing the electrons farther away from the nucleus of the atom. At this point, the electrons are in a higher energy state than when the atom was at rest.

Since an atom's natural state is at rest, or relaxed, these electrons soon return to their normal orbits. When this happens, the excess energy held by the electrons is emitted in the form of light particles, or photons. In essence, the electron emissions become light energy, or radiated light.

To this point, the atom has absorbed energy via light, heat or electric stimulation and then released the absorbed energy in the form of radiated light. For a laser quality of light to occur, the light must become a single concentrated, coordinated beam of one specific wavelength. For this to happen, mirrors and lenses are placed inside the electrons' field.

As part of the controlled environment a lasing medium, or resonator, surrounds the working atoms. There are two types of resonator cavities: linear and ring. In linear cavities, mirrors are placed on both ends of the resonator. The mirrors cause the electrons to bounce back and forth. In ring cavities, the mirrors are placed at perpendicular angles. In order for a laser beam of light to exit the cavity, one of the mirrors is a half-silver mirror, meaning there's a small slit at its center from which the light is cast.

As a result of the electrons bouncing back and forth, they also bounce into each other. When this happens, a magnetic effect results in which energy levels transfer from one electron to another. These collisions serve to further intensify the light emissions taking place inside the cavity. The resonator cavity, in effect, becomes an amplifying medium, thereby creating a concentrated, coordinated beam of radiated light.

The placement of lenses inside the electron field serve to further concentrate the light beam. The type of lens used will depend on the laser strength desired.